A common building construction utilizes corrugated sheet metal members between floors. A layer of concrete is poured on top of the corrugated member to form a floor for the upper level. The ribs and channels on the under side of the corrugated member form a ceiling for the lower space. The corrugated sheet metal member may, for example, be eighteen gauge galvanized steel. The channels that are defined in the under side of the member are typically about three inches deep and either four or six inches wide. Some interior walls extend transversely across the ribs and channels of the ceiling. Tunnel openings having cross-sectional areas equal to the areas of the channels are formed above the top frame member (header) of the interior wall. These tunnel openings extend across the top of the wall, from one side to the other. A fire can travel through the tunnel openings unless they are closed off or blocked.
U.S. Pat. No. 5,913,788, granted Jun. 12, 1999, to Thomas R. Herren, discloses several ways of blocking the tunnel openings to prevent a fire from spreading from one side of the wall to the other side. There is a need for providing a better way of blocking the tunnel openings that is less time consuming and less labor intensive than the known ways of blocking the tunnel openings. The primary object of the present is to fill this need.